D is not necessarily a flaw. A theory can indeed be disproven by one single fact that is not compatible with it. If we theorize that "all swans are white" a single black swan would disprove this theory. In this argument, the author rejects one theory on the grounds that it lacks an element that the other theory has. This is not so much as citing a fct, but simply claiming that a theory is not acceptable on the grounds that it lacks something- despite never telling us what makes a theory acceptable or unacceptable.